The present invention relates to electronic communication systems and, more particularly, to sleep modes in asynchronous data communication schemes.
In the last decades, progress in radio and VLSI technology has fostered widespread use of radio communications in consumer applications. Mobile radios and other portable devices are common consumer devices.
Presently, the primary focus of wireless communication technology is on voice communication. This focus will likely expand in the near future to provide inexpensive radio equipment which can be easily integrated into mobile and stationary devices. For instance, radio communication can be used to create wireless data links and thereby reduce the number of cables used to connect electronic devices. Recently, a new radio interface called Bluetooth was introduced to replace the cables used to connect laptop computers, headsets, PDAs, and other electronic devices. Some of the implementation details of Bluetooth are disclosed in this application, while a detailed description of the Bluetooth system can be found in xe2x80x9cBLUETOOTHxe2x80x94The universal radio interface for ad hoc, wireless connectivity,xe2x80x9d by J. C. Haartsen, Ericsson Review No. 3, 1998.
Radio communication systems for personal use differ significantly from radio systems like the public mobile phone network. Public mobile phone networks use a licensed band which is fully controlled by the network provider and guarantee a substantially interference-free channel.
In contrast, personal radio communication equipment operates in an unlicensed spectral band and must contend with uncontrolled interference. One such band is the globally-available ISM (Industrial, Scientific, and Medical) band at 2.45 GHz. The band provides 83.5 MHz of radio spectrum. Since the ISM band is open to anyone, radio systems operating in this band must cope with several unpredictable sources of interference, such as baby monitors, garage door openers, cordless phones, and microwave ovens. Interference can be avoided using an adaptive scheme that finds an unused part of the spectrum. Alternatively, interference can be suppressed by means of spectrum spreading. In the U.S., radios operating in the 2.45 GHz ISM band are required to apply spectrum-spreading techniques if their transmitted power levels exceed about 0 dBm.
Bluetooth radios use a frequency-hop/time-division-duplex (FH/TDD), spread spectrum access scheme. This radio technology supports low-cost, low-power implementations. Frequency-hop systems divide the frequency band into several hop channels. During a connection, radio transceivers hop from one channel to another in a pseudo-random fashion. The instantaneous (hop) bandwidth is small in frequency-hop radios, but spreading is usually obtained over the entire frequency band. This results in low-cost, narrowband transceivers with strong immunity to interference. Occasionally, interference jams a hop channel, causing faulty reception. When this occurs, error-correction schemes in the link can recover lost data.
The channel is divided into time slots, or intervals of 625 xcexcs, wherein a different hop frequency is used for each slot. This results in a nominal hop rate of 1,600 hops per second. One packet can be transmitted per interval/slot. Subsequent slots are alternately used for transmitting and receiving, which results in a TDD scheme.
The channel makes use of several, equally spaced, 1 MHz hops. With Gaussian-shaped frequency shift keying (FSK) modulation, a symbol rate of 1 Mbit/s can be achieved. In countries where the open band is 80 MHz or broader, 79 hop carriers have been defined. On average, the frequency-hop sequence visits each carrier with equal probability.
Bluetooth radio communications are based on peer communications and ad-hoc networking. In peer communications, all units are equal and a hierarchical network with a fixed infrastructure of base stations and portable terminals is not required. There is no centralized control that provides resource and connection management and other support services. In ad-hoc networks, which are usually based on peer communications, any unit can establish a connection to any other unit within range.
One application for Bluetooth-enabled communication units is the replacement of cables that connect computing or communication devices, such as computers, printers, mobile terminals, and the like. For systems such as Bluetooth to replace cables, data traffic over the radio interface must be very flexible. The enabling protocol must support both symmetric and asymmetric traffic flows and synchronous and asynchronous clocking schemes. In Bluetooth, a flexible communication channel is achieved using a slot structure without an overriding multi-slot frame structure. Bluetooth divides the time domain into slots and Bluetooth-enabled units are free to allocate the slots as necessary for transmission or reception.
As in other mobile radio communication systems, one important issue in peer-to-peer and ad-hoc communications is power conservation in mobile terminals. Since the radio communication typically takes place between portable and mobile equipment, low power consumption is essential to preserve battery life.
In communication networks, like cellular networks, low power modes are supported by the control channels of the network base stations. Such power conservation schemes are described in U.S. Pat. No. 5,794,146 to Sevcik et al., U.S. Pat. No. 5,758,278 to Lansdowne, commonly-assigned U.S. Pat. No. 5,883,885 to Raith, and International Patent Publication No. WO 00/04738. The base stations are typically fixed and not subject to power limitations. Once the terminal is synchronized to the base station, the terminal can enter a very low power mode. While in a low power mode, the terminal periodically scans for a signal from the base station, with each scan lasting for a short period of time. The base station, which is not constrained by power limitations, can broadcast the control channel or beacon continuously. The terminal can reduce its standby power considerably without sacrificing response time. Similar techniques are used on cellular asynchronous data channels, such as General Packet Radio Service (GPRS), which uses a control channel to schedule packet deliveries. A method of power conservation in a battery-operated, portable device is also described in European Patent Publication No. EP 0 944 273 A1.
Ad-hoc radio communications schemes like Bluetooth lack a control channel concept. Reducing power consumption while the device is in idle mode (i.e., not connected) has been described in commonly assigned U.S. Pat. No. 5,940,431 entitled xe2x80x9cAccess Technique of Channel Hopping Communications System,xe2x80x9d to J. C. Haartsen and P. W. Dent, the disclosure of which is incorporated here by reference. However, reducing power consumption while terminals are connected but during pauses between asynchronous data bursts presents technical problems that are not trivial, particularly when both units have to minimize power consumption.
Accordingly, there is a need in the art for a system and method to reduce power consumption in radio units engaged in asynchronous data services. More particularly, there is a need for a system and method that allows the radio units to enter a sleep mode without requiring extra overhead.
In peer-to-peer radio communications supporting asynchronous services, it is desired to reduce the power consumption in mobile terminals during pauses between data bursts. When there is no traffic on the channel for a predetermined amount of time, the units enter a low duty cycle sleep mode in which they sleep most of the time and wake up periodically, with a period T, to scan the channel for a brief time. A unit can restart communications only at specific points in time which relate to the sleep period T. The scan cycle of one unit preferably corresponds to the restart cycle of the other unit. If, for several sleep cycles, traffic does not return, T can be increased. This process may be carried out in both units, but without the units communicating to each other when the adaptation occurs. Since the two units may not update T exactly at the same time, T cannot be varied in an arbitrary fashion and cannot be based on relative timing. Instead, the scan time is based on absolute timing. Switching from one sleep/scan period to another sleep/scan period is allowed only at predetermined points in time. To prevent collisions when both units want to restart communications, the scan/restart cycles should be staggered. Once communication has restarted, the sleep mode is left. Only a predetermined period of silence on the channel can force the unit(s) into the sleep mode, starting with the smallest T.
In accordance with the present invention, there is a system for conserving power in a portable radio device. The system includes a first unit having at least a transmitter, a second unit having at least a receiver, and a communication channel through which the first unit and the second unit can communicate. Each receiver is activated for a period of time to enable the unit to receive a signal followed by a period of time in which the receiver is deactivated and the unit is unable to receive the signal. A first timing means is associated with the first unit and a second timing means associated with a second unit. Each timing means is used to measure an amount of elapsed time since the signal was last received. The system includes a plurality of time thresholds wherein the period of time for which the receiver is deactivated is increased by a time interval associated with one of the plurality of time thresholds when the amount of elapsed time exceeds the time threshold.
In accordance with another aspect of the present invention, the first unit transmits a signal to the second unit to initiate communications. The signal is transmitted more than one time. A time interval between successive attempts by the transmitter to initiate communications is determined by the amount of elapsed time since the last communication with the second unit. The time interval is associated with a time threshold exceeded by the amount of elapsed time since the last communication.
In accordance with another aspect of the present invention, there is a system for conserving power in a portable radio network. The system includes a plurality of communication devices wherein at least one of the communication devices has a transmitter and at least one of the communication devices has a receiver. There is a communication channel through which the plurality of communication devices can communicate. Each receiver is activated for a period of time to enable the communication device to receive a signal followed by a period of time in which the receiver is deactivated and the communication device is unable to receive a signal. A first timing means is associated with one of the plurality of communication devices and a second timing means is associated with another of the plurality of communication devices. Each timing means is used to measure an amount of elapsed time since the signal was last received. The system includes a plurality of time thresholds wherein the period of time for which the receiver is deactivated is increased by a time interval associated with one of the plurality of time thresholds when the amount of elapsed time exceeds the time threshold.
In accordance with another aspect of the present invention, there is a method for conserving power in a portable radio device. The method comprises the steps of measuring a period of elapsed time beginning with the end of a transmission; comparing the period of elapsed time with a threshold; increasing a time period between successive activations of a radio transmitter if the elapsed time exceeds a threshold period; and increasing a time period between successive activations of a radio receiver if the elapsed time exceeds a threshold period.
In accordance with another aspect of the present invention, there is a communication system including a first communication device having at least a transmitter, a second communication device having at least a receiver, and a communication channel through which the first communication device and the second communication device can communicate. Each receiver is activated for a period of time to enable the communication device to receive a signal followed by a period of time in which the receiver is deactivated and the communication device is unable to receive a signal. A first timing means is associated with the first communication device and a second timing means associated with a second communication device. Each timing means is used to measure an amount of elapsed time since the signal was last received. A plurality of time thresholds wherein the period of time for which the receiver is deactivated is increased by a time interval associated with one of the plurality of time thresholds when the amount of elapsed time exceeds the time threshold.
In accordance with another aspect of the present invention, there is a communication device which includes a receiver capable of interfacing with a communication channel through which the communication device can receive a signal. The receiver is activated for a period of time to enable the communication device to receive a signal followed by a period of time in which the receiver is deactivated and the communication device is unable to receive a signal. A timing means is associated with the communication device wherein the timing means is used to measure an amount of elapsed time since the signal was last received. The timing means compares the amount of elapsed time with a plurality of time thresholds wherein the period of time for which the receiver is deactivated is increased by a time interval associated with one of the plurality of time thresholds when the amount of elapsed time exceeds the time threshold.
In accordance with another aspect of the present invention, there is a method of operating a communication system having a transmitting device, a receiving device, a first timing means associated with the transmitting device, a second timing means associated with the receiving device, and a communication channel through which the transmitting device transmits a signal to the receiving device. The method comprising the steps of activating the receiving device at periodic intervals; increasing the period between successive activations of the receiving device based on an elapsed time since the last communication with the transmitting device; activating the transmitting device at periodic intervals to establish communication with the receiving device; and adjusting the period between successive activations of the transmitting device to coincide with the periods of activation of the receiving device.